A simplistic word picture of the sequence
is an energetic "Do Loop" that travels around the globe, much
as an "inchworm" might circle a tomato. The (upper ocean) locus
of the "tail" of the process provides the base direction for
the "front end" which reaches up and outward (with many degrees
of freedom) to determine the next "landfall". As the selection
is made, and the "front end" reattaches, the "tail"
is brought up to, but not over the landing spot, to begin again the process.

Think of the "tail end" as starting
at a particularly energetic location within the Warm Pool. That location
expells a large amount of its energy, upward, and eastward, and usually
poleward, only to resettle where cooler context is located. Meanwhile,
everywhere under the shadow of the "inchworm's" cloudy corpus,
an extra amount of heat is absorbed, leading toward a new, more energetic
state. Wherever a "tail end" has departed, the local heat (energy)
content has been substantially diminished. The thermal signatures will
reflect this.

Meanwhile, all downstream locations will
have been affected by the "shadow", or the clouds formed, and
will have gained energy, generally leading toward more "Deep Convection" expulsions.

Let's start again with the Pacific Warm
Pool, as a base location, with the easterly surface winds pushing west
from across the eastern Pacific, where they have scoured both sensible
heat and moisture (latent heat), thereby causing continous upwelling (shoal
thermoclines) from east to west. Thermocline depths in the eastern Pacific
are relatively shoal, with the 15C isotherm often within the photic zone
(90m or less). In the western Warm Pool region, the ocean receives both
stored (rainfall) and sensible heat, and through simple gravitational forces,
attains deeper thermoclines as these processes accrete. It is not uncommon
for the 15C isotherm in the midst of the Warm Pool to be found at depths
of several hundred meters (350-500m). Between the equator and the Inter-Tropical
Convergence Zone (the ITCZ is the seasonal atmospheric equator), the surface
temperature gradient is warmest in the west, and cooler in the east. This
is due to simply the surface easterlies, and a gradient of cloud cover.

Fishery and physiological responses to
ENSO warming - and suppression of production - is nearly immediate, either
in the open ocean or along coastlines.

As a consequence of ENSO warming and resulting
enhanced cloud cover, there are usually lower light levels, as well as
higher surface temperatures, and other related dynamics associated with
clouds and humidity. Pelagic food webs are often perturbed. Larger predators
must move to more productive areas, or die. When there is decreasing predation
from higher trophic level predators, emergent production tends to be spread
throughout lower trophic components. These smaller species are often in
competition with early life history stages of the migratory pelagic fishes,
or even become their major predators, leading to a period of decreased
survival for all but the most isolated of these fish larvae.

Also, stress-related spawning of adult
pelagic fishes is induced by the warmer temperatures, and their growth
patterns are foreshortened. Biomass production slows, as most of the energy
that they obtain or have stored is mobilized for reproduction. The resulting
eggs and larvae are of lower energy content, and therefore less likely
to survive the general fray for food, and predator avoidance.

As a primary general consequence of local
warming and suppression of upwelling, the more mobile species tend to become
concentrated, increasing competition, and providing both natural predators
and fishers with optimal forage conditions. For example, this year, the
Peruvian fishers were able to catch over 700,000 tons of anchoveta in one
week. All this from hundreds of unrefrigerated vessels that operate within
only a few travel hours of their three major home ports. In the 1972 El
Niño catches were similarly affected, and the combination of events
described above caused havoc within the region's ecosystems, and fisheries.

That was not the entire story, as the
fishes had begun a general decline in the late 1960s, as part of a decadal
scale climate regime change. There was a general slowing upwelling along
the coast of South America, that induced onshore intrusion of oceanic water,
and associated species. The resulting shifts in production centers, and
species, is well described. The recent (1985-1991) reversion to a stronger
coastal upwelling shifted the catches from sardines that emerged in the
warmer, lesser upwelling period, back to anchoveta.